Functional analysis of the murine coronavirus genomic RNA packaging signal

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Coronaviruses exhibit selective packaging of genomic RNA into virions, despite abundant subgenomic RNAs in infected cells.
• The mouse hepatitis virus (MHV) packaging signal (PS) is a known RNA structure involved in packaging defective interfering RNAs.
• The MHV PS is located within the replicase gene, encoding a subunit of the viral replicase-transcriptase complex.

Purpose of the Study:

• To investigate the function and mechanism of the MHV packaging signal (PS) at its native genomic location.
• To elucidate the role of PS RNA secondary structure in genomic RNA selection for virion packaging.

Main Methods:

• Construction and analysis of MHV viral mutants with alterations, deletions, or transpositions of the packaging signal (PS).
• Assessment of viral RNA packaging efficiency and composition in wild-type and mutant viruses.
• Evaluation of viral viability and growth kinetics in the presence and absence of a functional PS.

Main Results:

• Disruption or ablation of the PS secondary structure led to the packaging of substantial amounts of subgenomic RNAs alongside genomic RNA.
• The PS maintained its packaging function even when moved to a different location within the viral genome.
• MHV mutants lacking the PS were viable and showed no severe defects in viral growth, but exhibited reduced competitiveness.

Conclusions:

• The packaging signal (PS) is essential for the accurate selection of genomic RNA for coronavirus virions.
• The PS confers a selective advantage to MHV, enabling it to outcompete viruses lacking this element.
• The PS is not strictly required for MHV replication but plays a key role in viral fitness and competitive success.